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SEER, EER, and AHRI ratings

What's going on here? Comsumers are confused by the "up to" ratings that manufacturers advertise, yet AHRI ratings tell quite a different story. By looking at AHRI ratings I've come to some generalizations:

1: EER is much more important than SEER since EER is based on a 15 degree difference (95OD/80ID) between indoor and outdoor tempatures vs. SEER 2 degree (82OD/80ID)difference. I want to know how efficient it's running when it's HOT outside.

2: There is a practical EER limit of about 14 for air source AC units, no matter what the SEER is. EER increases significantly going from lower SEER to higher SEER single stage units. The larger outdoor coils improve EER. once the larger coil is used, EER is only marginally improved when going to 2 stage units.

3: The highest EER ratings are given to the smaller sized unit within a particular line. Downsizing has a real advantage here if the AC can keep up with the load during peak conditions.

4: Airhandler and coils make a big difference in EER, even on lower cost single stage units. 2 stage units almost always require variable speed blowers to get thier rated SEER.

It seems to me that consumers are better off buying smaller high SEER single stage equiptment and using the extra money to fix ductwork/leaks in the house. A 16 SEER 2 ton Single stage AC has about the same EER as a 3 ton 2 stage 19 SEER unit. If the house only has a 2 ton load the customer wasted thier money on a 2 stage unit as far as reducing power bills is concerned.

Are customers real world power bills that much lower with 2 stage equipment only because thier old stuff was in poor shape? Would thier power bills been just as low with a higher SEER single stage unit? Is 2 stage equipment more about comfort and less about energy savings?

i would say that you are comparing apples with onions which does not make sense.

eer is more or less obsolete figure, and the fact that some manufacturer does not declare seer says much about that manufacturer.

the mentioned ratings serve to give feel of possible energy savings. eer gives performance at one single specific set of operating conditions, which is arbitrary referent condition, and you can easily say that such condition will possibly not occur in more than few days in a year.

seer is attempting to simulate the whole season and give you average efficiency.

so it is contrary to what you state at your point 1. - having good rating on extreme conditions only can easily mean you will have average or even bellow-average rating at other conditions which may have much, much more occurrences during the cooling season.

That 15 degree difference probably looks a lot more like 90OD/75ID for the southern climates. People don't generally set thier AC @ 80, 75 is more typical. That would put the SEER rating based on 77 outdoor/75 indoors. If it's 77 outside, my AC is off and I open the windows to enjoy the nice day. I'm thinking that a typical AC has many more run hours over the course of a summer with tempatures over 90 then there is tempatures under 77.

Manuafactures DO declare SEER, but it's typically an "up to" number. That "up to" number is based on using a varible speed blower on a unit under 3 tons. Very few AC units under 3 tons are installed with VS blowers. 2 speed AC units under 3 tons are like unicorns, you rarely see one installed regardless of the actual cooling load.

Something to consider is the load on the system... it changes with many conditions:
*Humidity
*Occupancy of the structure
*Activity of occupants
*Time of day
*Landscape (did a significant tree fall due to a storm)
*Level of comfort desired
and many others.
So to look at this strictly as a mathematical equation is like saying a Chevy is better than a Ford (or visa-versa) simply because one model gets 1 MPG better than another in one year.

In all fairness... some folks really do not care (or even notice) anything beyond 'Is it hot or is it cold'... so to them the nicer details are irrelevant or even not noticed.
To a person who does not care about indoor RH (humidity), a VS furnace is a waste. To a person who truly appreciates subtle details of comfort, a 2 stage heat/2 stage AC with active humidity and dehumidity is worth the $$$.

As said: different strokes for different folks.

Back on the topic of the first post: IMO the conclusion is not particularly scientific due to the void of many details and expectations.